/**
 * Copyright (C) 2005-2009 Alfresco Software Limited.
 *
 * This file is part of the Spring Surf Extension project.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.extensions.webscripts;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

/**
 * Generator for GUID values. Can use either a basic Random (default) or
 * SecureRandom source for time based MD5 random GUIDs.
 * <p>
 * This code borrows concepts from RandomGUID. RandomGUID was written by Marc A.
 * Mnich and is available here: www.JavaExchange.com
 * 
 * @author Kevin Roast
 */
public final class GUID
{
    /** The value after MD5 before toString() processing */
    private String valueAfterMD5;
    
    private static final Random myRand;
    private static final SecureRandom mySecureRand;
    
    private static final String unid;
    
    static
    {
        mySecureRand = new SecureRandom();
        myRand = new Random(mySecureRand.nextLong());
        try
        {
            unid = InetAddress.getLocalHost().toString();
        }
        catch (UnknownHostException e)
        {
            throw new IllegalStateException(e);
        }
    }

    /**
     * Instantiates a new object guid.
     */
    public GUID()
    {
        getRandomGUID(false);
    }

    /**
     * Instantiates a new object guid.
     * 
     * @param secure    true to use SecureRandom
     */
    public GUID(boolean secure)
    {
        getRandomGUID(secure);
    }

    /**
     * Gets the random guid.
     * 
     * @param secure    true to use SecureRandom
     * 
     */
    private void getRandomGUID(final boolean secure)
    {
        final StringBuilder beforeMD5 = new StringBuilder(64);
        beforeMD5.append(unid)
                 .append(':')
                 .append(Long.toString(System.currentTimeMillis()))
                 .append(':')
                 .append(Long.toString(secure ? mySecureRand.nextLong() : myRand.nextLong()));
        
        try
        {
            final MessageDigest md5 = MessageDigest.getInstance("MD5");
            md5.update(beforeMD5.toString().getBytes());
            
            final byte[] array = md5.digest();
            final StringBuilder sb = new StringBuilder(32);
            for (int j = 0; j < array.length; j++)
            {
                sb.append(hex[(array[j] & 0xFF)]);
            }
            
            valueAfterMD5 = sb.toString();
        }
        catch (NoSuchAlgorithmException e)
        {
            throw new IllegalStateException(e);
        }
    }
    
    @Override
    public String toString()
    {
        return valueAfterMD5.toString();
    }
    
    public static String generate()
    {
        return new GUID().toString();
    }
    
    public static String generate(final boolean secure)
    {
         return new GUID(secure).toString();
    }
    
    private final static String[] hex = {
        "00", "01", "02", "03", "04", "05", "06", "07",
        "08", "09", "0a", "0b", "0c", "0d", "0e", "0f",
        "10", "11", "12", "13", "14", "15", "16", "17",
        "18", "19", "1a", "1b", "1c", "1d", "1e", "1f",
        "20", "21", "22", "23", "24", "25", "26", "27",
        "28", "29", "2a", "2b", "2c", "2d", "2e", "2f",
        "30", "31", "32", "33", "34", "35", "36", "37",
        "38", "39", "3a", "3b", "3c", "3d", "3e", "3f",
        "40", "41", "42", "43", "44", "45", "46", "47",
        "48", "49", "4a", "4b", "4c", "4d", "4e", "4f",
        "50", "51", "52", "53", "54", "55", "56", "57",
        "58", "59", "5a", "5b", "5c", "5d", "5e", "5f",
        "60", "61", "62", "63", "64", "65", "66", "67",
        "68", "69", "6a", "6b", "6c", "6d", "6e", "6f",
        "70", "71", "72", "73", "74", "75", "76", "77",
        "78", "79", "7a", "7b", "7c", "7d", "7e", "7f",
        "80", "81", "82", "83", "84", "85", "86", "87",
        "88", "89", "8a", "8b", "8c", "8d", "8e", "8f",
        "90", "91", "92", "93", "94", "95", "96", "97",
        "98", "99", "9a", "9b", "9c", "9d", "9e", "9f",
        "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7",
        "a8", "a9", "aa", "ab", "ac", "ad", "ae", "af",
        "b0", "b1", "b2", "b3", "b4", "b5", "b6", "b7",
        "b8", "b9", "ba", "bb", "bc", "bd", "be", "bf",
        "c0", "c1", "c2", "c3", "c4", "c5", "c6", "c7",
        "c8", "c9", "ca", "cb", "cc", "cd", "ce", "cf",
        "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7",
        "d8", "d9", "da", "db", "dc", "dd", "de", "df",
        "e0", "e1", "e2", "e3", "e4", "e5", "e6", "e7",
        "e8", "e9", "ea", "eb", "ec", "ed", "ee", "ef",
        "f0", "f1", "f2", "f3", "f4", "f5", "f6", "f7",
        "f8", "f9", "fa", "fb", "fc", "fd", "fe", "ff"
    };
}
